My $.02
Using radiosity for something like that is really only going to be feasible if you have a very simple scene, like what you posted. If you plan on having a scene with hundreds of these lights in a strand, the time it’ll take to calculate a radiosity solution from that will just be ridiculous.
Personally, I’d just suggest placing an omni light in the center of your light shape - maybe two, if you need a more accurate form. Adjust the lights (especially their falloff settings), and if you need shadows be sure uncheck shadow casting for your light object. I’d also model the filaments of the bulbs (as splines), and give them a self-illuminating material. I’d probably create a sphere around the filament as well, to composite out a layer to use for applying a glow in post.
My main suggestion is to just try and keep it simple. You can get great results with a simple setup if you tweak everything correctly. If you’re going to be doing an extreme close-up of the bulbs, then sure, give the bulb full raytraced reflections, throw in a GI or radiosity solution from the filament, add in some IBL and just go nuts with the rendering settings. But if you’re going to use it for anything else, most of that is going to be unusable, and a waste of time really.